Confocal Microscopy of Luminescence Inhomogeneity in LGSO:Ce Scintillator Crystal

Confocal microscopy was exploited to study spatial distribution of luminescence characteristics in Lu
₂
SiO
₅
:Ce (LSO:Ce) and mixed Lu
_2x
Gd
_2-2x
SiO
₅
:Ce (LGSO:Ce) crystals. Spatial distributions of spectrally-integrated photoluminescence (PL) intensity, PL band peak and spectral center of mass positions, and band width were determined. In both crystals, the luminescence spectra at 405 nm excitation are dominated by one broad band peaked at ~ 510 nm, while a long-wavelength shoulder is also observed in LGSO:Ce. Spatial inhomogeneities of the order of 1-3 micron in diameter are observed for the band position in LGSO:Ce. A comparative analysis of the spectra shows that the inhomogeneity is caused by spatial distribution in the spectral component at 500-700 nm, which may be attributed to Ce
³⁺
located in CeO
₆
polyhedra (Ce2), or, more probably, to some defects in the crystal. Our results indicate that the changes in luminescence spectrum shape reflect Lu/Gd ratio fluctuations on a micrometer scale in the bulk of the mixed LGSO:Ce crystals.